The invention relates to a device for arc welding, in particular submerged-arc welding, with one or several fusible electrodes which are in each case supplied from an alternating-current source with falling characteristic and are advanced by a feed means, the feed rate being regulated by a regulator, which is supplied with the arc voltage as the actual value for the arc length, in such a manner that the arc length is constant.
Compared with arc welding using a direct-current source with a nearly horizontal voltage/current characteristic, arc welding using an alternating-current source with a falling characteristic has advantages and disadvantages. In the case of arc welding with a horizontal characteristic, the feed means can be set to a constant feed rate. The arc length remains essentially constant in this case because, if the arc voltage is constant, the tendency towards a smaller distance of the electrode from the workpiece is countered by increased current intensity and thus greater deposition rate because of the horizontal characteristic. This advantage is opposed by the disadvantage that the magnetic fields of the arcs have an unfavourable effect on each other when closely adjacent. In addition, the simultaneous operation of several electrodes with direct current requires a return line which has correspondingly large dimensions.
The demand for high deposition efficiencies is met by the simultaneous use of several electrodes. Such requirements occur with deposit welding and especially with profiling welding in which a workpiece is virtually generated only from the welding material. Not infrequently, more than twelve electrodes are simultaneously used.
Investigations with a device of the type initially mentioned have shown that with the simultaneous use of several electrodes, the arc length of which is regulated in accordance with the arc voltage, the deposition efficiencies of the individual electrodes are different despite equal current intensity at all electrodes. The result of these different deposition efficiencies are welding beads of different height produced by the electrodes used next to each other. With several deposit layers, this leads to large dimensional differences. In addition, the different deposition efficiencies have the effect that the initially identical wire lengths are used up after periods of different length. In practice, this means that the reels carrying the wire must be changed either at different times or with lengths still remaining on the reels.